In recent years, a heat-resistant material that does not contain halogen, phosphorous, and so on from the standpoint of protecting environment but is frame-resistant and to which Pb-free solder can be attached has been desired to be used as a board material. On the other hand, in market trends of downsizing, weight reduction, and function advancement of electronic devices, higher integration and surface mounting of semiconductor devices have advanced year by year. For example, an area-mounting semiconductor device such as a ball-grid array has been newly developed as a next-generation semiconductor device so as to fill the need for higher pin count and higher speed that have approached limits in surface-mounted semiconductor devices typified by QFP and SOP.
The area-mounting semiconductor device is assembled in the following process. First, a semiconductor element is mounted on one side of a circuit board, and only the semiconductor element mounting surface, that is, one side of the board is molded and encapsulated by an epoxy resin composition or the like. After that, processing (reflow processing) is carried out in which Pb-free solder balls are attached at a temperature of 230° C. to 260° C. to a surface of the circuit board on which the semiconductor element is not mounted. Further, processing in which the area-mounting semiconductor device is mounted on a substrate (secondary mounting processing) is carried out to manufacture an electronic device.
Thus, the material of the circuit board is required to have the property of high elastic modulus in heating so as to improve the ease of mounting during the reflow processing. Moreover, if a large amount of distortion occurs due to thermal expansion, stress on the board increases, and thus the circuit board is required to have the property of low coefficient of thermal expansion. On the other hand, at room temperature, even a thin board is required to have high stiffness. That is, the material of the circuit board (hereinafter referred to as “board material”) is required to have the property of being highly heat-resistant, that is, the property of having a high glass transition temperature (Tg). For this reason, board materials having such properties are being developed.
On the other hand, if the circuit board is a thin type board with a thickness of not more than 500 μm, when the semiconductor element mounting surface is to be molded and encapsulated by an epoxy resin composition or the like, a large warp occurs due to cure shrinkage contraction of the epoxy resin composition or the like. The prior art that the semiconductor element mounting surface is encapsulated by a resin encapsulating layer with a low coefficient of thermal expansion so as to reduce the amount of warp is known (see, for example, Japanese Laid-open Patent Publication (Kokai) No. 2000-216299).
However, according to the prior art, although the amount of warp in the circuit board before the reflow processing can be reduced, the amount of warp occurring after the reflow processing cannot be reduced. For this reason, there is the problem that a semiconductor device cannot be manufactured in a stable manner.
For example, if a semiconductor device is manufactured using the above described board material having high elastic modulus in heating and high Tg as described above, a convex warp rounded downward with both ends regarded as reference positions, that is, a so-called smile warp occurs in the semiconductor device as shown in FIG. 12A before the reflow processing, and the warp inverts to become a convex warp rounded upward with both ends regarded as reference positions, that is, a so-called cry warp as shown in FIG. 12B after the reflow processing. In general, it is difficult to secondarily mount the semiconductor device in which such a cry warp has occurred on a substrate, and thus the problem that the yield during the secondary mounting processing deteriorates arises.
An object of the present invention is to provide a circuit board manufacturing method and a semiconductor manufacturing apparatus that make it possible to manufacture a next-generation semiconductor device in a stable manner and improve the yield during secondary mounting processing.